This invention relates to an impact dot head for an impact dot matrix printer and a method of manufacturing same and, in particular to, an impact dot head having a nose surface flush with a top end guide surface of the impact dot head which can be easily and efficiently manufactured.
Referring to FIG. 1, wherein the prior art impact dot head having a top end guide surface 102a facing a printing medium 106 is provided. Top end guide surface 102a of a top end guide 102 is recessed in a nose surface 101a of a nose 101. In this configuration, when an activated printing wire 105 is caught by a stepped portion 106a of a printing medium 106, the projecting length L of printing wire 105 is large between top end guide surface 102a and printing medium 106. In this manner, a great amount of stress is applied to a printing wire root 105a causing printing wire 105 to be susceptible to breakage. On the other hand, if top end guide surface 102a projects from nose surface 101a, an ink ribbon 107 is sandwiched between top end guide 102 and a ribbon mask 108.
Consequently, the relationship between the parts of the impact dot head creates a number of problems. For instance, the running or driving property of ink ribbon 107 declines. The feeding capabilities of ink ribbon 107 deteriorate. Abrasion of top end guide 102 is induced due to the friction created by ink ribbon 107. Accordingly, it is desirable for nose surface 101a to be flush with top end guide surface 102a.
Reference is now made to FIG. 2 which depicts a further conventional impact dot head. In this example, a top end guide 202 and middle guides 203 slidably maintain printing wire 201. Guides 202, 203 are retained by a nose guide 204. In order to make a surface 202a of top end guide 202 on the side of a printing medium 207 flush with a surface 205b of a nose 205 on the same side, a spacer 206 is interposed between a positioning surface 205a of nose 205 and a positioning surface 204a of nose guide 204. The thickness of spacer 206 is then adjusted to construct the flush relation between surface 202a and surface 205b.
FIG. 3 shows another conventional embodiment of an impact dot head. After measuring a thickness t of a top end guide 302, top end guide 302 is then bonded to nose 301 having a stepped portion 301a equivalent to the thickness t of top end guide 302. After measuring and bonding, the surfaces of top end guide 302 and nose 301 are flush with each other. Additionally, a machine cut may be made after bonding top end guide 302 to nose 301 to make the surfaces flush with respect to each other.
The conventional impact dot head depicted in FIG. 2 presents a number of problems. The manufacturing process takes an inordinate amount of time to measure a distance D1 from nose surface 205b to surface 205a and a distance D2 from top end guide surface 202a to nose guide surface 204a. These measurements are then used to determine the thickness of spacer 206, select the suitable spacer 206 and finally insert spacer 206 into the impact dot head. With the requirements of all these measurements, mass production is both difficult and costly.
There are also production problems inherent in the construction of the impact dot head disclosed in FIG. 3. This impact dot head requires an excessive amount of time to measure and select the thickness t of top end guide 302 and also a depth d of a groove 301a of nose 301 in which top end guide 302 is inserted. Therefore, mass-production of the impact dot head is hard to attain as well as being quite costly. The method of manufacturing nose 301 and top end guide 302 flush with each other by machining the surfaces causes wire guide hole 302b to be deformed. Thus, massproduction is again both difficult and costly.
It is, therefore, desirable to provide an impact dot head having the nose surface flush with the top end guide surface to improve the durability thereof, while at the same time permitting mass production of the impact dot head at a relatively low cost.